Infoscience

Poster

Bacterial life in a stagnant PCE-contaminated aquifer

Chlorinated ethenes (CEs) represent a major environmental concern in most industrialized countries. These compounds, used as solvents and degreasing agents since the 1940s, have been released accidentally into the environment. Being recalcitrant to aerobic biodegradation, they are nowadays persisting in the form of dense non-aqueous phase liquids (DNAPLs) and are slowly diffusing in aquifers, threatening drinking water resources. Dehalorespiration is a bacterial anaerobic respiration in which the sequential reduction of CEs to the final harmless ethene is coupled with energy production. This bacterial metabolism represents a promising way to bio-remediate anoxic CE-contaminated aquifers, by the means of monitored or enhanced natural attenuation. The drawback of this approach is that dechlorination end product is often not known a priori. Natural attenuation by the means of dehalorespiration may therefore lead to the undesired accumulation of dichloroethylene and/or vinyl chloride, which are even more toxic than the original tetrachloethylene (PCE) or trichloroethylene. The understanding of the dehalorespiration ecology in a specific groundwater environment (i.e. the relationships between the dehalorespiring bacterial guild and other functional microbial guilds, and with local environmental conditions, such as groundwater flow, aquifer recharge, electron donors, etc.) is therefore a prerequisite to the design of an adapted remediation strategy. Here we studied the specific case of an anoxic, PCE-contaminated aquifer, with a very slow groundwater flow, in which dehalorespiration has been shown to occur. Groundwater samples have been collected in two successive campaigns. DNA-based bacterial communities were analyzed at different locations on the site using T-RFLP profiling, together with the analysis of multiple environmental factors. Using statistical multivariate analyses, we characterized the respective influence of the contaminants on the bacterial communities and proposed a conceptual model of the bacterial ecology in stagnant anoxic CE-contaminated aquifers.

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